Vehicles which are specifically constructed and used for transporting and delivering hydrocarbon fuel, principally by road but also possibly by rail, often include a main tank portion which is divided into a plurality of discrete tank compartments in which different fuel types may be separately contained. Thus a first tank compartment may, for example, contain gasoline (petrol) and a second tank compartment may contain diesel. Further distinctions are possible in that, for example, different gasoline grades (standard or high octane) may be carried in different tank compartments on the same vehicle. In another example, fuels of the same type but which attract different rates of duty (tax) may be carried in different tank compartments of the same vehicle. By way of example, in the UK diesel fuel sold for certain uses (such as for agricultural vehicles) has a lower rate of tax than diesel sold to the general public, and to provide a distinction a colourant is added to the lower tax diesel fuel. Tank compartments of the vehicle may also be used to convey other fuels such as kerosene.
It is clearly important when a using vehicle having a plurality of tank compartments which may contain different fuels that, at the location of delivery, the correct fuel is dispensed so that mixing of different fuels is prevented. A typical scenario would be replenishment of the fuel tanks at a filling station (service station or gas station) where, for example, it is vital that gasoline contained in a tank compartment of the vehicle is not dispensed into a storage tank already containing some diesel fuel. It is therefore important for the vehicle operator to be able easily to ascertain or to check the identity of the fuel contained in a particular tank compartment of the vehicle before such fuel is dispensed. In other words, the operator must have means of knowing unambiguously the identity of the fuel contained in a given tank compartment of the vehicle before that fuel is dispensed.
It is noted that it is not commonly possible to distinguish between different fuel types by mere visual inspection. Also, any arrangements which require an operator to access the fuel (e.g. for sampling or insertion of measurement devices) through an access means (such as an openable and closeable lid) provided at the top of the tank are inherently disadvantageous because of the need for the operator to mount to the top of the tank, which can be a safety problem.
It is also advantageous to know the quantity of fuel in a tank compartment, for example for the purposes of determining how much fuel has been, or can be, dispensed from the compartment.
It can readily be appreciated that vehicles constructed for the transport and delivery of volatile hydrocarbon fuels must comply with strict safety requirements to prevent any possible ignition of the fuel, the consequences of which could be disastrous. These requirements apply in particular to any electrical equipment associated with the vehicle which must never be a possible source of ignition of the fuel. Legal and standards requirements determine other aspects of the construction of such vehicles, dealing for example with the strength of the tank and its ability to resist deformation and spillage in the event of an accident, provision for emergency services to drain fuel from the tank in an emergency situation, access requirements to the tank for inspection and maintenance, operating pressures and pressure relief arrangements and so on. It follows that constructional features and arrangements known for other goods conveyance containers or tanks may not be appropriate for use with hydrocarbon fuel tanks.
It is further noted that the fuel tank compartments of fuel delivery vehicles are frequently emptied and re-filled. Such emptying and re-filling can allow air to be mixed with the fuel contained in the tank compartment. Also, it is inevitable that the fuel contained within the tank compartment moves during transit, and such movement can be quite vigorous, depending on the motion of the vehicle. Such movement can also cause mixing of air (from the head space of the tank compartment) into the fuel. It follows that any measurement devices or the like inserted into or contained within the fuel tank compartment should be configured to withstand the motion of the fuel and operate correctly despite such motion, and more especially should remain effective and function correctly in the event that air becomes mixed in the fuel.
For the avoidance of doubt, the present disclosure is not concerned with devices intended to measure parameters such as quantity or identity of fuel contained in the fuel tank of a vehicle, or being dispensed into or from such a fuel tank. By “fuel tank” in this context is meant the tank or vessel of a vehicle provided for the purpose of supplying fuel to the engine of the vehicle and thus used for propulsion of the vehicle.
Devices for measuring the quantity of fluid in a compartment based on pressure measurements are, in general terms, known.